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The Las Vegas Sun’s reporting on lethal bacteria in hospitals is based on analysis of Nevada hospital data collected by the state from 1999 to 2009.

Nevada law requires that the data, which are based on hospital billing records and contain the same information the facilities use to get paid by insurance companies, be accurate and collected for analysis. The Sun requested the information, which is public but had not been released for public review, from state officials who archive it. Nevada is one of at least 40 states that collect similar data.

The records used by the Sun do not contain information that could identify patients — there are no names, birth dates, addresses or admission dates. The records also lack clinical details such as doctor notes or medical histories.

That’s not to say the data aren’t detailed. They are based on medical records and include diagnoses, procedures, billed charges for each admission and length of stay. The 2.9 million records analyzed essentially summarize what was wrong with the patient and what was done.

The Sun’s analysis of the data in 2008 and 2009 largely hinges on billing codes that indicate whether a medical condition was “present on admission.” Such codes have been required for acute-care hospitals since 2008. This allowed the Sun to identify infections that the hospitals reported as occurring after patients were admitted.

To identify cases of Methicillin-resistant Staphylococcus aureus, or MRSA, the Sun’s strategy was twofold:

Before fiscal year 2009, which began in October 2008, no diagnosis coding for MRSA infection existed — there were only diagnoses to indicate an S. aureus infection with no direct detail about whether it was susceptible to antibiotics. To identify likely MRSA cases, the Sun looked for patient discharge records that also had a diagnosis code of “V09.0,” which identifies an infection with microorganisms resistant to penicillins. This is widely considered by coding experts to be the only way to identify MRSA.

Beginning in fiscal 2009, specific MRSA diagnosis codes were used in the discharge data, so the Sun used them for the remainder of the analysis.

To identify cases of Clostridium difficile, or C. diff., the Sun examined records where the patient specifically had a diagnosis for intestinal infection caused by Clostridium difficile.

The data were also used for the first part of this ongoing series, “Health care can hurt you,” in June. That story investigated 969 events of harm suffered at Las Vegas hospitals in 2008 and 2009.

The Sun sent each of the hospitals being reviewed a spreadsheet of MRSA and C. diff. cases that had been identified in the discharge records, including the cases identified as acquired in the facility, seeking comment. No hospital disputed the Sun’s findings.